Preserve cross references in the USFM cross references fields

[johnml1135]

We should just preserve cross references in the cross reference fields (https://ubsicap.github.io/usfm/notes_basic/xrefs.html#) including \r (which is sometimes used as a cross reference as well). Users can use regex's to update to a different format if they want to - it will be more reliable than NLLB - and I would rather have a standard formatting thing they have to do than to look for the weird errors.